A bolometer is a type of sensor used to measure electromagnetic radiation. A bolometer generally comprises an absorptive element that is connected via a thermal link to a heat sink or thermal reservoir (i.e. a body of constant or near-constant temperature). A thermometer or other temperature sensitive element is attached to or embedded into the absorptive element in order to measure a temperature of the absorptive element. In some bolometers, the absorptive element may itself be the temperature sensitive element.
The essential operating principle of a bolometer is that, when incident electromagnetic radiation or photons are absorbed by the absorptive element, the energy from the radiation raises the temperature of the absorptive element. The change in temperature is measured by the temperature sensitive element in order to measure a magnitude of the absorbed radiation. In order to detect certain types of radiation, the absorptive element can be configured for sensitivity to different ranges of wavelengths.
FIG. 1 shows a microbolometer 100 for detecting infrared radiation 104. The microbolometer 100 includes an absorber 108 which comprises a material configured to absorb infrared radiation and exhibit relatively changes in resistance as a result of small changes in temperature. For example, the absorber 108 may comprise of amorphous silicon or vanadium oxide. The absorber 108 is suspended above a substrate 112 by a pair of electrodes 116 in order to thermally isolate the absorber 108 from the substrate 112. A current or voltage is applied to the absorber 108 via the electrodes 116 and changes in resistance of the absorber 108 are monitored in order to detect the radiation 104.
One common use for a sensor such as the microbolometer 100 is for measuring thermal radiation. Objects at any non-zero temperature radiate electromagnetic energy. At temperatures near room temperature, objects primarily radiate infrared radiation, which can be detected by a sensor, such as the microbolometer 100. However, it would be advantageous to use bolometer sensors to implement other kinds of sensors, beyond simple radiation sensors.